1. Field of the Invention
The present invention relates to tools coated by amorphous carbon films having wear resistance and an anti-adhesion feature, said tools including cutting-off tools (represented by cutters, knives, and slitters) and indexable inserts used for example in turning tools and face milling cutter and milling cutters (exemplified by drills, endmills, and reamers).
2. Description of the Background Art
Conventional cutting tools and wear-resistant tools have hard coatings on the surface of substrates to enhance wear resistance and the protection of the tool surface. The substrates consist of such known materials as a WC-based sintered hard alloy, cermet, and high-speed steel. It is also known that the hard coatings comprise either a single layer or multiple layers of one or more of titanium carbide, hafnium carbide, zirconium carbide, titanium nitride, hafnium nitride, zirconium nitride, titanium carbonitride, hafnium carbonitride, zirconium carbonitride, and aluminum oxide that are produced through physical vapor deposition or chemical vapor deposition.
In recent trends, however, cutting tools are used in operation at a higher speed to improve processing efficiency, thus increasing the temperature on the cutting edges thereof. Demands for specific improvements in tool materials have also become stringent. It is therefore essential to produce hard coatings that are more stable at high temperatures, that is, more oxidation-resistant and more adhered to the substrates. In addition, it has also become of growing importance to enhance the wear resistance of the hard coatings, namely hardness, for longer life of the cutting tools.
Particularly in fields where high levels of hardness and strength are required, a tool comprising a substrate formed from one of a cubic boron nitride sintered body, a diamond sintered body, a silicon nitride sintered body, or an aluminum oxide-titanium carbide sintered body is used. A tool having said hard coating on the surface of the substrate has been proposed.
For example, Japanese Patent Laying Open No. Tokukaihei No. 7-18415 proposes a cBN-based ceramic cutting tool covered by a single hard layer or multiple hard layers having an average thickness of 5 μm to 20 μm. Said single hard layer is formed from one selected from the group of TiC, TiN, TiCN, TiCO, TiCNO, and Al2O3, while said multiple hard layers consist of two or more of the same group. Japanese Patent Laying Open No. Tokukaihei No. 8-119774 also proposes a tool incorporating a substrate of either a cBN sintered body or a diamond sintered body, and at least one hard and thermal-resistant layer thereon to cover at least the tool part relevant to the cutting process. Said layer contains at least one element of C, N, and O, together with the primary constituents of Ti and Al.
In recent years, workpiece materials to be cut have become diverse, including such soft metals as aluminum alloys; nonferrous metals including titanium, magnesium, and copper; organic materials; materials containing hard particles like graphite; printed circuit boards; and the combination of a ferrous material and aluminum for bi-metallic cutting. Bi-metallic cutting is herein defined as the simultaneous cutting process of a ferrous material adhered to aluminum. In machining the workpiece materials herein listed, the edge of a cutting tool is susceptible to such accumulation and adhesion of said workpiece materials that increase cutting resistance. In some cases, the cutting edge is chipped during the process. These specific workpiece materials tend to cause far greater wear of the cutting tool than do other workpiece materials.
Diamond tools have conventionally been used in specific applications including the processing of soft metals such as aluminum and aluminum alloys, nonferrous metals represented by titanium, magnesium, and copper, materials containing hard particles like graphite, organic materials, printed circuit boards; and the bimetallic cutting of a ferrous material adhered to aluminum. Tools having diamond films formed on substrates tend to have a rough surface due to the polycrystalline structures of the films. It is necessary, therefore, to polish the tool surface for applications in precision processing.
However, as a diamond film is the hardest among the existing materials, there is no other alternative but to use diamond for surface polishing, and this has made the cost higher.
TiN or other ceramic films obtained through physical vapor deposition are usually as thick as 2 μm to 3 μm. On the other hand, a diamond film needs to have a thickness of 20 μm to 30 μm initially. This is due to the fact that diamond crystals grow at greatly varying speeds depending on their crystal orientation and the formed film is subjected to polishing to obtain a smoother surface. In addition, it is necessary to carry out etching and remove graphite that also grows during the diamond film deposition. This has decreased the film formation speed to one-tenth of the speed that ceramic coats require, and made the production including the coating process extremely expensive.
As with a tool wherein one of a diamond sintered body, a cBN sintered body, a silicon nitride sintered body, or an aluminum oxide-titanium carbide sintered body is brazed to a substrate, there has existed the problem of providing a complicated shape and a diameter as small as a few millimeters. When applied to a cutting tool, those materials are insufficiently tough so as to cause the cutting edge thereof to chip easily, abruptly ending the short lifetime.
Thus the present invention mainly aims to provide amorphous carbon coated tools for applications including the machining of soft metals, nonferrous metals, organic materials, materials containing hard particles, printed circuit boards, and the bimetallic cutting of a ferrous material adhered to a soft metal. As the tool surface has an excellent smooth feature, said tools effectively protect the cutting edges from chipping and cause less corroded workpiece materials to accumulate thereon. Furthermore, a high thermal conductivity of said tools curbs a temperature increase on said cutting edges and enables applications under severe conditions such as dry cutting and high-speed machining. Another object of the present invention is to provide the method of producing said tools.